Part Load Vortex Rope as a Global Unstable Mode

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Simon Pasche ◽  
François Avellan ◽  
François Gallaire
Keyword(s):  
Flow Field ◽  
Large Scale ◽  
Vortex Breakdown ◽  
Control Strategies ◽  
Renewable Energy Sources ◽  
Vortex Rope ◽  
Part Load ◽  
Spiral Vortex ◽  
Electrical Generation ◽  
Operation Flexibility

Renewable energy sources (RES) have reached 23.7% of the worldwide electrical generation production in 2015. The hydraulic energy contribution amounts to 16.6% and comes mainly form large-scale hydropower plants, where Francis turbines represents 60% of the generating units. However, the future massive development of RES will require more advanced grid regulation strategies that may be achieved by increasing the operation flexibility of the Francis generating units. Part load operating condition of these turbines is hindered by pressure fluctuations in the draft tube of the machine. A precessing helical vortex rope develops in this condition, which imperils the mechanical structure and limits the operation flexibility of these turbines. A thorough description of the physical mechanism leading to the vortex rope is a prerequisite to develop relevant flow control strategies. This work, based on a linear global stability analysis of the time-averaged flow field, including a turbulent eddy viscosity, interprets the vortex rope as a global unstable eigenmode. In close resemblance to spiral vortex breakdown, a single-helix disturbance develops around the time-averaged flow field and growths in time to finally form the vortex rope. The frequency and the structure of this unstable linear disturbance are found in good agreement with respect to the three-dimensional (3D) numerical flow simulations.

scholarly journals Robustness Comparison of Synthetic Inertia Strategies for Doubly Fed Induction Generators under Different Operating Conditions

2020 ◽  
Author(s):  
Paulo Andrade Souza ◽  
Renan R. dos Santos ◽  
Manoelito C. N. Filho ◽  
Daniel Barbosa ◽  
Luciano Sales Barros
Keyword(s):  
Wind Energy ◽  
Large Scale ◽  
Control Strategies ◽  
Renewable Energy Sources ◽  
Operating Conditions ◽  
Wind Condition ◽  
Primary Control ◽  
Parameter Uncertainties ◽  
Doubly Fed ◽  
Frequency Behavior

Due to the increasing penetration of Renewable Energy Sources (RES) such as wind energy in electrical grids, Wind Energy Conversion Systems (WECS) participation in primary control is becoming required including the Doubly Fed Induction Generator (DFIG)-based WECS. High integration of large scale DFIG-based WECS brings new challenges to their primary control support, and more strongly due to the wind condition and grid parameter uncertainties. One of the most used types of control strategy for DFIG-based WECS primary support is the synthetic inertia, however, robustness of these techniques have not been tested. In this work three synthetic inertia control strategies will be tested under different operating conditions of wind speed, frequency and voltage sag. For testing the DFIG-based WECS, it was modeled on ATP including its control systems and the results quantified the controllers robustness on the tested controllers with respect to transient frequency behavior.

Structural sensitivity of spiral vortex breakdown

2013 ◽  
Vol 720 ◽  
pp. 558-581 ◽  
Author(s):  
Ubaid Ali Qadri ◽  
Dhiren Mistry ◽  
Matthew P. Juniper
Keyword(s):  
Stability Analysis ◽  
Passive Control ◽  
Stokes Equations ◽  
Vortex Breakdown ◽  
Control Strategies ◽  
Axial Component ◽  
Azimuthal Mode ◽  
Global Mode ◽  
Structural Sensitivity ◽  
Spiral Vortex

AbstractPrevious numerical simulations have shown that vortex breakdown starts with the formation of a steady axisymmetric bubble and that an unsteady spiralling mode then develops on top of this. We investigate this spiral mode with a linear global stability analysis around the steady bubble and its wake. We obtain the linear direct and adjoint global modes of the linearized Navier–Stokes equations and overlap these to obtain the structural sensitivity of the spiral mode, which identifies the wavemaker region. We also identify regions of absolute instability with a local stability analysis. At moderate swirls, we find that the $m= - 1$ azimuthal mode is the most unstable and that the wavemaker regions of the $m= - 1$ mode lie around the bubble, which is absolutely unstable. The mode is most sensitive to feedback involving the radial and azimuthal components of momentum in the region just upstream of the bubble. To a lesser extent, the mode is also sensitive to feedback involving the axial component of momentum in regions of high shear around the bubble. At an intermediate swirl, in which the bubble and wake have similar absolute growth rates, other researchers have found that the wavemaker of the nonlinear global mode lies in the wake. We agree with their analysis but find that the regions around the bubble are more influential than the wake in determining the growth rate and frequency of the linear global mode. The results from this paper provide the first steps towards passive control strategies for spiral vortex breakdown.

scholarly journals Grid-forming control strategies for blackstart by offshore wind farms

2020 ◽  
Author(s):  
Anubhav Jain ◽  
Jayachandra N. Sakamuri ◽  
Nicolaos A. Cutululis
Keyword(s):  
Power System ◽  
Wind Power ◽  
Power Plants ◽  
Large Scale ◽  
Wind Farm ◽  
Control Strategies ◽  
Renewable Energy Sources ◽  
Stability Limit ◽  
Offshore Wind ◽  
Wind Power Plants

Abstract. Large-scale integration of renewable energy sources with power-electronic converters is pushing the power system closer to its dynamic stability limit. This has increased the risk of wide-area blackouts. Thus, the changing generation profile in the power system necessitates the use of alternate sources of energy such as wind power plants, to provide blackstart services in the future. This however, requires grid-forming and not the traditionally prevalent grid-following wind turbines. In this paper, four different grid-forming control strategies have been implemented in an HVDC-connected wind farm. A simulation study has been carried out to test the different control schemes for the different stages of energization of onshore load by the wind farm. Their transient behaviour during transformer inrush, converter pre-charge and de-blocking, and onshore block-load pickup, has been compared to demonstrate the blackstart capabilities of grid-forming wind power plants for early participation in power system restoration.

scholarly journals Fault Analysis using SFCL in the Convertor System at the Load Line

2021 ◽  
pp. 60-67
Author(s):  
Suman Baghel ◽  
Sanjeev Jarring
Keyword(s):  
Large Scale ◽  
Low Voltage ◽  
Control Strategies ◽  
Short Circuit ◽  
Renewable Energy Sources ◽  
Short Circuit Current ◽  
Fault Analysis ◽  
Residual Current ◽  
Operating Conditions ◽  
The Impact

Among many renewable energy sources, solar energy is considered one of the most promising resources for large-scale electricity generation. Here propose resistive SFCL if a fault occurs in a simple low voltage (LV) network. To assess the impact of SFCL in the power system under study, the space-time approach is used to evaluate the short-circuit current in force and spurious control strategies are suggested to achieve the goal. The results complement the feasibility of the proposed A-ACO-based rationalization control for transmission activity according to the limiting circuit and fault current analyzer. The second model of the bastard chassis concludes that the chassis with residual current limiting circuit and analyzer reduces the expansion of the residual current and prevents the voltage from dropping to zero, that no artificial and temporal innovation is used as before. Intelligence-based computer procedures further shorten the working time, which also makes the frame more efficient, as the voltage is restored to its typical value in a short time if the test frame is played for 1 second in a MATLAB climate / SIMULINK. The time taken by the ACO algorithm to restore normal operating conditions in the line was 0.197 seconds, 0.206 seconds and 0.27 seconds for LLLG, LLG and LG errors, respectively.

Optimal Control of Part Load Vortex Rope in Francis Turbines

2019 ◽  
Vol 141 (8) ◽  
Author(s):  
Simon Pasche ◽  
François Avellan ◽  
François Gallaire
Keyword(s):  
Optimal Control ◽  
Systematic Approach ◽  
Draft Tube ◽  
Vortical Flow ◽  
Vortex Rope ◽  
Part Load ◽  
Precessing Vortex Core ◽  
Hydraulic Machines ◽  
Optimal Force ◽  
Operation Flexibility

The mitigation of the precessing vortex core developing in the draft tube of Francis turbines operating under part load conditions is crucial to increase the operation flexibility of these hydraulic machines to balance the massive power production of intermittent energy sources. A systematic approach following the optimal control theory is, therefore, presented to control this vortical flow structure. Modal analysis characterizes the part load vortex rope as a self-sustained instability associated with an unstable eigenmode. Based on this physical characteristic, an objective function targeting a zero value of the unstable eigenvalue growth rate is defined and subsequently minimized using an adjoint-based optimization algorithm. We determine an optimal force distribution that successfully quenches the part load vortex rope and sketches the design of a realistic control appendage.

scholarly journals A Scalable Control Strategy for CHB Converters in Photovoltaic Applications

Energies ◽  
2021 ◽  
Vol 15 (1) ◽  
pp. 208
Author(s):  
Álvaro Pérez Mayo ◽  
Ainhoa Galarza ◽  
Asier López Barriuso ◽  
Javier Vadillo
Keyword(s):  
Control Strategy ◽  
High Speed ◽  
Power Plants ◽  
Large Scale ◽  
Pulse Width Modulation ◽  
Control Strategies ◽  
Renewable Energy Sources ◽  
Bridge Model ◽  
Zero Sequence ◽  
Modular Converters

Renewable energy sources are becoming more relevant in recent decades in power generation, leading to investment in developing efficient systems. Specifically, in photovoltaic energy, modular converters are attracting interest since their characteristics enable them to work at high voltage and optimize the generated energy. However, the control strategies found the literature limit the scalability potential of modular converters. The main aim of this paper is to propose a scalable control strategy for a grid-tied CHB (Cascaded H-Bridge) converter for large-scale photovoltaic power plants. The control proposed is able to take full advantage of converter scalability and modularity, being based on the parameters needed for bipolar sinusoidal PWM (Pulse Width Modulation), and thus reducing the calculus required and simplifying its implementation. Power imbalances are overcome including the zero-sequence vector injection to allow power exchange between phases. Furthermore, the parameter used for power factor control has been discretized and discretization time analysis shows that the control strategy is stable and does not require a high-speed communication channel. For validation purposes, simulations are conducted on a downsized 12 H-bridge model.

scholarly journals Grid-forming control strategies for black start by offshore wind power plants

2020 ◽  
Vol 5 (4) ◽  
pp. 1297-1313 ◽  
Author(s):  
Anubhav Jain ◽  
Jayachandra N. Sakamuri ◽  
Nicolaos A. Cutululis
Keyword(s):  
Power System ◽  
Wind Power ◽  
Power Plants ◽  
Large Scale ◽  
Control Strategies ◽  
Renewable Energy Sources ◽  
Stability Limit ◽  
Offshore Wind ◽  
Advantages And Disadvantages ◽  
Wind Power Plants

Abstract. Large-scale integration of renewable energy sources with power-electronic converters is pushing the power system closer to its dynamic stability limit. This has increased the risk of wide-area blackouts. Thus, the changing generation profile in the power system necessitates the use of alternate sources of energy such as wind power plants, to provide black-start services in the future. However, this requires grid-forming and not the traditionally prevalent grid-following wind turbines. This paper introduces the general working principle of grid-forming control and examines four of such control schemes. To compare their performance, a simulation study has been carried out for the different stages of energization of onshore load by a high-voltage direct-current (HVDC)-connected wind power plant. Their transient behaviour during transformer inrush, converter pre-charging and de-blocking, and onshore block-load pickup has been compared and analysed qualitatively to highlight the advantages and disadvantages of each control strategy.

Predictive control of spiral vortex breakdown

2018 ◽  
Vol 842 ◽  
pp. 58-86 ◽  
Author(s):  
S. Pasche ◽  
F. Gallaire ◽  
F. Avellan
Keyword(s):  
Objective Function ◽  
Predictive Control ◽  
Vortex Breakdown ◽  
Control Strategies ◽  
Three Dimensional ◽  
The Self ◽  
Mean Flow ◽  
Volume Force ◽  
Spiral Vortex ◽  
The Mean

The predictive control of the self-sustained single spiral vortex breakdown mode is addressed in the three-dimensional flow geometry of Ruithet al.(2003) for a constant swirl number$S=1.095$. Based on adjoint optimization algorithms, two different control strategies have been designed. First, a quadratic objective function minimizing the radial velocity intensity, taking advantage of the physical mechanism underpinning spiral vortex breakdown. The second strategy focuses on the hydrodynamic instability properties using as objective function the growth rate of the most unstable global eigenmode. These minimization algorithms seek for an optimal volume force in an axisymmetric domain avoiding therefore expensive three-dimensional computations. In addition to considering eigenvalues around the base flow, we also investigate the stability around the mean flow and we find that it correctly predicts the frequency of the self-sustained single spiral vortex breakdown mode for Reynolds numbers up to$Re=500$. Close to the instability threshold, at a Reynolds value of$Re=180$, all these control strategies successfully quench the spiral vortex breakdown. The related volume force is found identical for the base and mean flow eigenvalue control even if the uncontrolled growth rates differ significantly. The control of the least unstable eigenvalue of the mean flow is not only found optimal at$Re=180$, it also stabilizes the flow at a Reynolds value as large as$Re=300$, which opens promising extensions to industrial applications.

Flow Field Investigation in Draft Tube of Francis Turbine at Off-Design Operation Using a Vortex Identification Algorithm

2021 ◽  
Author(s):  
Sandeep Kumar ◽  
Subodh Khullar ◽  
Bhupendra K. Gandhi
Keyword(s):  
Flow Field ◽  
Vortex Breakdown ◽  
Draft Tube ◽  
Field Investigation ◽  
Francis Turbine ◽  
Identification Algorithm ◽  
Deep Part ◽  
Vortex Identification ◽  
Stagnation Region ◽  
Part Load

Abstract At off-design operations, flow instabilities such as vortex breakdown, reverse flows, and stagnant regions are observed in Francis turbines. The present work shows the numerical flow field investigations of a Francis turbine at two different part loads (PL) by employing a vortex identification algorithm. The analysis has been performed at various locations in the draft tube by extracting the velocity fields at different time steps of the simulation. The first operating point involves a fully developed rotating vortex rope (RVR) in the draft tube, which precesses at a frequency of 0.28 times of the runner rotation. The present algorithm is able to identify the regions along with the eccentric local rotation center. The second operating regime shows characteristics of deep part load with central solid body rotation in the draft tube flow field. The results show highly swirling flows with very low axial velocity. The flow is confined primarily near the walls. The analysis shows that the extent of stagnation region at deep part load is more and no inner shear layer is present as compared to the part-load operation. The spatial harmonic decomposition (SHD) of the pressure data is also performed to evaluate the synchronous and asynchronous components of pressure pulsations.

scholarly journals Real-Time Sensorless Robust Velocity Controller Applied to a DC-Motor for Emulating a Wind Turbine

Energies ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 868
Author(s):  
Onofre A. Morfin ◽  
Riemann Ruiz-Cruz ◽  
Jesus I. Hernández ◽  
Carlos E. Castañeda ◽  
Reymundo Ramírez-Betancour ◽  
...  
Keyword(s):  
Power Systems ◽  
Wind Turbine ◽  
Feedback Linearization ◽  
Large Scale ◽  
Renewable Energy Sources ◽  
Time Derivative ◽  
Dc Motor ◽  
Induction Generator ◽  
Main Challenge ◽  
Electrical Generation

The wind power systems of variable velocity using a doubly-fed induction generator dominate large-scale electrical generation within renewable energy sources. The usual control goal of the wind systems consists of maximizing the wind energy capture and streamlining the energy conversion process. In addition, these systems are an intermittent energy source due to the variation of the wind velocity. Consequently, the control system designed to establish a reliable operation of the wind system represents the main challenge. Therefore, emulating the operation of the wind turbine by means of an electric motor is a common strategy so that the controller design is focused on the induction generator and its connection to the utility grid. Thus, we propose to emulate the dynamical operation of a wind turbine through a separately excited DC motor driving by a sensor-less velocity controller. This controller is synthesized based on the state-feedback linearization technique combined with the super-twisting algorithm to set a robust closed-loop system in the presence of external disturbances. A robust velocity observer is designed to estimate the rotor velocity based on the armature current measuring. Furthermore, a robust differentiator is designed for estimating the time derivative of the velocity error variable, achieving a reduction in the computational calculus. Experimental tests were carried using a separately excited DC motor coupled with a dynamometer to validate the proposed wind turbine emulator.

Sign in / Sign up

Export Citation Format

Share Document